转换为Swift 3错误，未解包的可选类型的值

Question

使用Swift 2编写的代码可以使用但不适用于Swift 3.

ShoppingManager.getShoppingItemsForPage(currentPage, pageSize: 40) { (shopItems: [ShopItemModel]?, error: Error?) -> () in
        if error == nil {

...

self.shopItems.append(Array(shopItems[10..<40]))

我收到错误

value of optional type [ShopItemModel] not unwrapped。

我尝试使用?，但它不起作用。

这是我的ShopItemModel

class ShopItemModel: NSObject {
    //RestKitMapping
    var itemID: String?
    var shopName: String?

Answer 1

使用guard let语句展开你的shopItem，否则你可以使用!强制解包，但如果shopItems为零则会崩溃

guard let shopItemArray = shopItems else {
    return  // shopItems is nil if it goes here
}

self.shopItems.append(Array(shopItemArray[10..<40]))

Answer 2

编译：

ShoppingManager.getShoppingItemsForPage(currentPage, pageSize: 40) { (shopItems: [ShopItemModel]?, error: Error?) -> () in
    if error == nil {
        let lastItem = self.shopItems.count

        if self.currentPage == 1 {
            self.shopItems.append(contentsOf: Array(shopItems![10..<40]))
        } else {
            self.shopItems.append(contentsOf: Array(shopItems!))
        }